I can think of many good reasons for the US to go ahead with the nuclear deal with Iran, and I can think of just as many reasons not to. So, if you're confused, let me see if I can confuse you even more.

The proposed deal to lift sanctions on Iran - in return for curbs on its bomb-making capabilities so that it would take at least a year for Teheran to make a weapon - has to be judged in its own right. I will be looking closely at the quality of the verification regime and the specificity of what happens if Iran cheats.

But the deal also has to be judged in terms of how it fits with wider American strategic goals in the region, because a US-Iran deal would be an earthquake that touches every corner of the Middle East. Not enough attention is being paid to the regional implications - particularly what happens if the US were to strengthen Iran at a time when large parts of the Sunni Arab world are in meltdown.

The Obama team's best argument for doing this deal with Iran is that, in time, it could be "transformational".

That is, the ending of sanctions could open Iran to the world and bring in enough fresh air - Iran has been deliberately isolated since 1979 by its ayatollahs and Revolutionary Guard Corps - to gradually move Iran from being a revolutionary state to a normal one, and one less inclined to threaten Israel.

If one assumes that Iran already has the know-how and tools to build a nuclear weapon, changing the character of its regime is the only way it becomes less threatening.

The challenge to this argument, explains Mr Karim Sadjadpour, a Middle East specialist at the Carnegie Endowment, is that while the Obama team wants to believe this deal could be "transformational", Iran's supreme leader Ali Khamenei "sees it as transactional" - Iran plugs its nose, does the deal, regains its strength and doubles-down on its longstanding revolutionary principles. But, then again, you never know. What starts out as transactional can end up being transformational in ways that no one can prevent or predict.

A second argument is that Iran is a real country and civilisation, with competitive (if restricted) elections, educated women and a powerful military. Patching up the relationship could enable America to better manage and balance the Sunni Arab Taleban in Afghanistan, and counterbalance the Sunni jihadis, like those in the Islamic State of Iraq and Syria (ISIS), now controlling chunks of both countries.

The United States has relied heavily on Saudi Arabia ever since Iran's 1979 revolution, and while the Saudi ruling family and elites are aligned with America, there is a Saudi Wahhabi hard core that has funded the spread of the most puritanical, anti-pluralistic, anti-women form of Islam that has changed the character of Arab Islam and helped to foster mutations like ISIS. There were no Iranians involved in the Sept 11, 2001 attacks.

Then again, it was Iranian agents who made the most lethal improvised explosives in Iraq that killed many American troops there. And it was Iran that encouraged its Iraqi Shi'ite allies to reject any extended US military presence in Iraq and to also overplay their hand in stripping power from Iraqi Sunnis, which is what helped to produce the ISIS counterreaction.

"In the fight against ISIS, Iran is both the arsonist and the fire brigade," added Mr Sadjadpour. To Saudi Arabia, he added, the rise of ISIS is attributable to the repression of Sunnis in Syria and Iraq by Iran and its Shi'ite clients. To Teheran, the rise of ISIS is attributable to the financial and ideological support of Saudi Arabia and its Gulf allies.

And they are both right, which is why US interests lie not with either the Saudis or the Iranian ideologues winning, but rather with balancing the two against each other until they get exhausted enough to stop prosecuting their ancient Shi'ite-Sunni, Persian-Arab feud.

Then again, if this nuclear deal with Iran is finalised, and sanctions lifted, much more Iranian oil will hit the global market, suppressing prices and benefiting global consumers. Then again, Iran would have billions of dollars more to spend on cyberwarfare, long-range ballistic missiles and projecting power across the Arab world, where its proxies already dominate four Arab capitals: Beirut, Baghdad, Damascus and Sanaa.

But, given the disarray in Yemen, Iraq and Syria, do we really care if Iran tries to play policeman there and is embroiled in endless struggles with Sunni militias?

For 10 years, it was America that was overstretched across Iraq and Afghanistan. Now it will be Iran's turn. I feel terrible for the people who have to live in these places, and the US should certainly use air power to help prevent the chaos from spreading to islands of decency like Jordan, Lebanon and Kurdistan in Iraq. But managing the decline of the Arab state system is not a problem America should own. We've amply proved that we don't know how.

So before you make up your mind on the Iran deal, ask how it affects Israel, the country most threatened by Iran. But also ask how it fits into a wider US strategy aimed at quelling tensions in the Middle East with the least US involvement necessary and the lowest oil prices possible.

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